Math · Ratios & measurement
Estimation, Rounding, and Answer Checks
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Start here: key ideas
- The named place determines which digit stays.
- The next digit decides whether the kept digit changes.
- Compatible numbers make mental arithmetic easier.
- An estimate checks magnitude; it does not replace an exact answer when precision is required.
What you’ll be able to do
- Round a value to a specified place.
- Choose compatible numbers for a useful estimate.
- Use estimates and practical count limits to reject implausible answers.
The named place determines which digit stays. The next digit decides whether the kept digit changes.
Round one stated place
To round, locate the requested place. Look one digit to its right. If that digit is 5–9, add 1 to the rounding digit; if it is 0–4, keep it. Replace following whole-number digits with zeros or drop following decimal digits. Thus 47,368 to the nearest hundred is 47,400 because the tens digit is 6.
Do not round every digit in sequence. For 2.449 to the nearest tenth, inspect the hundredths digit, 4, and report 2.4.
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